As an added motivation for shedding those extra kilos, the proposal is to produce Bathroom Scales that also feature an indication of the average lifespan / age of death for various weights.

I'm not quite sure how statistically valid you could get (obviously there are a lot of factors in how long
you're going to live), but I'd suggest there is sufficient correlation between increased weight and reduced lifespan to validly introduce the parallel "estimated lifespan" scale.

Imagine watching those kilos go up while your estimated age of death creeps down... scary enough to make you take your health/weight more seriously.